A brain structure for language pathways found only in humans and higher primates has now also been identified in apes. The new, controversial study barely published in Nature Neuroscience suggests that the origins of language may have appeared 20-25 million years earlier than previously thought.
Compared to other animals, the human brain has uniquely adapted to language. Our ability to produce speeches, listen and communicate between us is unmatched. To understand it we must know its origins, and know how we got here.
Unfortunately, brain tissue is not preserved for very long, so it is difficult to know when the first building blocks of language appeared in our distant past. Today, if they want to locate this “ghost fossil” of the brain, scientists must rely largely on our still-living “cousins.”
Studies on the origins of language
So far, brain imaging studies in chimpanzees have revealed a language circuit similar to humans, but the idea that monkeys also have something similar was hotly contested.
Now, some researchers say it's because we searched the wrong place. While neuroscientists have focused on the prefrontal cortex and temporal lobes, the origins of our language would lie in the auditory cortex of rhesus macaques.
A hidden treasure
“I admit that we were amazed to see a similar pathway hidden in plain sight within the auditory system of nonhuman primates,” says the neuropsychologist Chris Petkov from the University of Newcastle, UK.
It's like finding a new fossil from a long lost ancestor.
If researchers are right with this newfound missing link, the first neural building blocks for the evolution of language may have appeared much earlier than we thought.
The last common ancestor of macaques and humans lived around 25-30 million years ago, and it is long before the ancestor we share with chimpanzees, who lived only 5 million years ago.
The origins of human language
Human language is generally produced and perceived along a central linguistic path, known as arched fasciculus (AF), which embraces the prefrontal cortex and the temporal lobe.
Over the years, however, we have realized that this circuit is much more complex than we once thought. It is connected to many other brain regions, and some research suggests that the auditory cortex plays a key role.
By comparing the brains of humans, higher primates and monkeys with new imaging data, the new study was able to identify FA in the auditory complex of both halves of the human brain and determine that it was more developed on the left side than the right one.
They then showed a similar (albeit less pronounced) path that existed in the same areas both in the brains of macaques and chimpanzees.
From language linked to hearing to “total” language
Noting how the connection has evolved differently in humans, the authors argue that our language system seems to have moved away from such a great dependence on the auditory path, involving multiple temporal and parietal areas of the brain.
“There was something special about this journey. The link with the projection from the auditory system to regions of the frontal cortex, which supports language in humans, is fascinating. So we were honestly surprised to find it there and see that both types of monkeys have their own version of this pathway as well.”
In summary: of course, the origins of human language are completely unique. However, these results suggest that we are not alone with sophisticated levels of auditory cognition and voice communication.
The potential of this discovery
This finding could be enormous for treating human patients with neurological problems. The language can be spoken, written or typed, (in the future transmitted with thought), so even if a stroke patient can no longer communicate through one of these ways, perhaps there are other intact language paths that can still be accessed.
There is still a lot to do
It's an exciting premise, but there's still a lot to test. Brain imaging studies cannot tell us everything we need to know, and further research will need to explore this auditory pathway in more detail.
Even Petkov himself admitted that this missing brain fossil is “highly controversial”. But given how much good it could do, he thinks it's "important to learn more."
